Thin film formation apparatus

ABSTRACT

The present invention relates to relates to a hydrogenated amorphous silicon carbide used as the surface protecting layer of the photosensitive member for electrohotographic apparatus. In view of not allowing generation of blurring of photosensitive member under the high humidity atmosphere, the content (x) of carbon in the hydrogenated amorphous silicon carbide expressed by the general formula a-Si 1-x  C x  :H is in the range of 0.4≦x≦0.8 and a ratio (TO/TA) of the peak (TO) amlitude appearing in the vicinity of 480 cm -1  and the peak (TA) amplitude appearing in the vicinity of 150 cm -1  observed by the laser Raman spectroscopy measurement using the excitation laser of Ar +  488 is set to 2.0 or higher.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 07/756,591,filed Sep. 9, 1991, now abandoned, which application is a division ofapplication Ser. No. 07/405,297, filed Sep. 11, 1989, now U.S. Pat. No.5,122,431.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methodology and apparatus for formingthin film hydrogenated amorphous material, for example, hydrogenatedamorphous silicon, hydrogenated amorphous carbon, hydrogenated amorphoussilicon carbide and thin film transistor (TFT) material.

2. Description of the Related Art

Thin film hydrogenated amorphous materials, particularly materialsformed from hydrogenated amorphous silicon (hereinafter referred to asa-Si:H) are widely used as electrophotographic photosensitive membersfor electrophotographic apparatus to form images upon irradiation withan information light beam since such materials have excellent durabilityand are not sources of environmental pollution.

As shown in FIG. 1, a photosensitive member consisting of a blockinglayer 103 for carrier injection, a carrier generation and transportlayer 104 and a surface protecting layer 105 layered sequentially onto aconductive substrate 100 such as aluminum (Al).

Blocking layer 103 for carrier injection is formed from a P type or Ntype a-Si:H, a-SiO:H, a-SiC:H or a-SiN:H material, and photosensitivelayer 104 is formed from an a-Si:H material. The surface protectinglayer 105 is made from a-SiC:H, a-SiN:H or a-SiC:H:F. Particularly, forthe surface protecting layer 105, and a-SiC:H or a-SiN:H material havinga wide band gap is used but a-SiC:H is superior from a hardnessviewpoint.

However, Si in the surface layer reacts with oxygen in the air to formSiO which is hydrophilic and blurring may thus result under highhumidity conditions.

Therefore, in the past the photosensitive materials have been heated orfilms which do not contain Si in the surface layer have been employed.

However, in cases where the photosensitive member is heated, it isnecessary to include a heating source in the electrophotographicapparatus, thereby complicating the configuration of theelectrophotographic apparatus and increasing its cost.

On the other hand, when the surface layer does not include Si, lighttransmissivity, hardness and suitability for use as a photosensitivemember are diminished.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a photosensitivea-SiC:H material which assures high light transmissivity, hardness andsuitability for use as a photosensitive member and which is able toresist blurring under high humidity conditions without using a heatingsource.

Accordingly, the present invention provides a hydrogenated amorphoussilicon carbide having a general formula a-Si_(1-x) C_(x) :H wherein theratio of the TO peak amplitude appearing in the vicinity of 480 cm⁻¹observed by laser Raman spectroscopy measurement using an Ar⁺ 488 nmexcitation laser to the TA peak amplitude appearing in the vicinity of150 cm⁻¹ is 2.0 or more and the carbon content (x) is in the range of0.4 to 0.8.

In accordance with the invention, investigations have been conducted todetermine the surface behavior of an a-Si:H photosensitive membersubjected to corona irradiation under high humidity conditions bymeasurement of the contact angle using high sensitivity reflection FT-IR(IR-RAS) techniques. These investigations have shown that coronairradiation of the surface protecting layer of an a-Si:H photosensitivemember under high humidity conditions causes an increase of Si--OH,HO--OH, Si--O--Si, NO₃ -- and CO₃ ---- at the surface, thereby enhancingwettability. Ozone (O₃) generated by corona irradiation directlyoxidizes the surface of the photosensitive member and increasesSi--O--Si coupling. Simultaneously, absorption groups such as NO₃ --,CO₃ ---- and OH are generated and such absorption groups adhere to Si atthe surface as hydrates. As a result, surface polarity and thus surfacewettability are increased because the polar H₂ O molecules tend toadhere to the surface. When the surface is charged under such condition,charges flow and therefore blurring occurs. In accordance with thepresent invention, wettability is improved (decreasing) by increasingthe carbon content in a-Si_(1-x) C_(x) :H films of the type that areused currently as the surface protecting layer because, as explainedabove, it is not practical to employ materials that do not include Si atthe surface to provide an a-Si photosensitive member which is resistiveto humidity.

Moreover, a-Si_(1-x) C_(x) :H materials having only a high carboncontent do not necessarily have sufficient carrier injection blockingcapability to be used as the surface protecting layer. Therefore, thepresent invention provides an a-Si_(1-x) C_(x) :H material with a carboncontent (x>0.4) which provides a value of 2.0 or more as the ratio ofpeak TO amplitude appearing in the vicinity of 480 cm⁻¹ observed bylaser Raman spectroscopy measurement using an Ar 488 nm excitation laserto the peak TA amplitude appearing in the vicinity of 150 cm⁻¹. Suchmaterial enables the provision of an a-Si_(1-x) C_(x) :H film which hasa high carbon content and sufficient blocking functionability to performas the surface protecting layer.

It is known that a-Si_(1-x) C_(x) :H films having high carbon content(x≧0.5) can be formed using the well known RF-CVD (Radio FrequencyChemical Vapor Deposition) apparatus (see, for example, U.S. Pat. No.4,507,375, and page 452 of "Electrophotographic Bases and Application",issued in 1988 by Corona Publishing Corp.). However, there is no mentionin these publications of the use of such films as blocking layers andthe disclosed films would not allow the application of charging voltagesbecause the density of film is deteriorated.

FIG. 2 is a schematic diagram showing the arrangement of an RF-CVDapparatus of the prior art.

In FIG. 2, a substrate 100 suitable for having an a-SiC:H film formedthereon is mounted on an electrode 27 connected to the ground in thereactor vessel 26. Reactor vessel 26 is evacuated by a rotary pump 33and a mechanical booster pump 32 connected to an outlet port 116.Meanwhile, the reactor vessel 26 is connected to a pipe 118 at inletport 114. Pipe 118 is then connected to a gas cylinder 1 containingdisilane Si₂ H₆ through a flow regulator 5a, to a gas cylinder 2containing propane C₃ H₈ through a flow regulator 5b, to a gas cylinder3 containing hydrogen H₂ through a flow regulator 5c and to a gascylinder 4 containing argon Ar through a flow regulator 5d.

The gases contained in gas cylinders 1, 2, 3 and 4 are introduced intoreactor 26 through pipe 118 for use as starting gases only in thequantities dictated by the adjustments of the respective flow regulators5a, 5b, 5c and 5d.

As the starting gases are introduced into the reactor 26 the radiofrequency power is supplied to the first electrode 29 from the radiofrequency power source 31 and a plasma of starting gases is formedacross the first and second electrodes 27, 29 and an a-SiC:H film isthus formed on the substrate 100.

The RF-CVD apparatus as described above may be used to form ana-Si_(1-x) C_(x) :H film having high content (x) of carbon simply byincreasing the flow rate of propane C₃ H₈ from gas cylinder 2, but thea-Si_(1-x) C_(x) :H film thus formed is not able to function as ablocking layer.

Accordingly, it is another object of the present invention to provide amethod and apparatus for forming an a-Si_(1-x) C_(x) :H film having thecharacteristics described above.

Therefore, according to the present invention, an apparatus for forminghydrogenated amorphous silicon carbide film is provided which comprisesa reactor vessel, means for introducing starting gases to the reactorvessel, means for generating plasma from the starting gases within thereactor vessel, separate means for introducing hydrogen gas into thereactor vessel and means for generating hydrogen radicals from thehydrogen gas introduced by the separate means.

In accordance with the invention, long life hydrogen radicals (.H) aregenerated by the decomposition of hydrogen gas (H₂) using a microwavefrequency (2.45 GHz, for example), and such radicals are sent into thereactor vessel and into the deposition space where the plasma is formedby decomposition of the starting gases. It is theorized that the densityof the deposited film is improved when the reaction surface iseffectively covered with hydrogen radicals (.H).

Atom coupling energy is as follows:

    ______________________________________                                        H--H > C--H >    C--C >   Si--C >                                                                              Si--Si >                                                                             Si--H                                 ______________________________________                                        4.88 eV                                                                              4.29 eV   3.58 eV  3.38 eV                                                                              3.10 eV                                                                              3.06 eV                               ______________________________________                                    

To increase the density of an a-Si_(1-x) C_(x) :H film during formationit is believed that the quantity of dangling Si atom bonds should bereduced. On the other hand, an increased bond ratio x causes a largerquantity of hydrogen to be coupled with carbon because of the couplingenergy relationships described above, and as a result of the increasedhydrogen-carbon coupling it is believed that the quantity of dangling Siatoms bonds correspondingly increases and the film is therebydeteriorated. In order to prevent such phenomenon, the presence ofdangling Si atom bonds is decreased, in accordance with the invention,by covering the reaction surface with an excess of hydrogen radicals(.H) and Si--C coupling is increased as a result of the increased amountof H--H re-coupling thus generated at the surface. Accordingly, thedensity of the film can be increased. In the past it has been proposedthat the density of the film can be increased by reducing hydrogen (H₂),but it has been found in accordance with the present invention that theblocking characteristics of an a-SiC:H film are not good when carboncontent is high. However, when hydrogen (H₂) is replaced by hydrogenradicals (.H), such radicals easily cover the surface because they aremore active than hydrogen (H₂) and the density of the film can beincreased even for films having higher contents of carbon.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawings. It is to beexpressly understood, however, that the drawings are for purposes ofillustration only and are not intended as a definition of the limits ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the make-up of a-Si photosensitivemember;

FIG. 2 is a schematic illustration of a prior art RF-CVD apparatus;

FIG. 3 is a schematic diagram illustrating the components of a thin filmformation apparatus which embodies the principles and concepts of thepresent invention;

FIG. 4 is a perspective view of the thin film formation apparatus ofFIG. 3;

FIG. 5 is a schematic diagram to explain the method of introducingpropane gas to the apparatus of FIG. 3;

FIG. 6 is an alternative thin film formation apparatus used forgenerating photosensitive member drums;

FIG. 7 is a graph showing the results of IR-RAS measurements;

FIG. 8 is a schematic diagram to explain the laser Raman spectroscopymeasuring apparatus;

FIG. 9 is a graph showing laser Raman spectroscopy measurement results;

FIG. 10 is a graph showing the relationship between carbon content andTO/TA ratio;

FIG. 11 is a schematic perspective view illustrating another embodimentof the present invention;

FIG. 12 is a schematic diagram illustrating a hydrogen radical inletport for the embodiment of FIG. 11;

FIG. 13 is a schematic view illustrating a further embodiment of theinvention;

FIG. 14 is a schematic diagram illustrating a hydrogen radical inletport for the FIG. 13 apparatus;

FIG. 15 is a graph plotting light emission intensity H against thedistance D between the plasma generating furnace and a substrate;

FIG. 16 is a schematic diagram illustrating yet another embodiment ofthe apparatus of the invention;

FIG. 17 is a schematic diagram illustrating a hydrogen radical generatorfor the apparatus of FIG. 16;

FIG. 18 is a graph showing laser Raman spectroscopy measurement results;

FIGS. 19 through 23 are schematic diagrams illustrating five additionalalternative forms of apparatus which embody the principles and conceptsof the invention; and

FIG. 24 is a schematic diagram illustrating the hydrogen radicalgenerating apparatus used in connection with the apparatus of FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 3 and 4, a thin film formation apparatus, generallydesignated by reference numerals 110 includes a reactor vessel 26 havinga first inlet port 114, a second inlet port 115 and an outlet port 116.Inlet port 114 is connected to one end of an inlet pipe 118, the otherend of which is connected to suitable starting gas sources 1, 2 and 6.Outlet port 116 is connected to a suitable vacuum pump comprising arotary pump 33 and a mechanical booster pump 32.

The inlet pipe 118 is connected to a gas source 1 containing disilane(Si₂ H₆) through a flow regulator 5a, to a gas source 2 containingpropane (C₃ H₈) through a flow regulator 5b and to a gas source 6containing diborane (B₂ H₆) through a flow regulator 5e. The diborane(B₂ H₆) is diluted with helium (He) so that it contains 100 ppm of He.

Inlet port 115 is connected to hydrogen radical generating means 120.Hydrogen radical generating means 120 includes a quartz pipe 23 havingone end 23a that is connected to inlet port 115 and another end 23b thatis connected to a gas source 7 to be described hereinbelow. Quartz pipe23 has a diameter of 30 mm and hydrogen (H₂) is supplied thereto from ahydrogen gas inlet port 25 at end 23b of the quartz pipe 23 via flowregulator 5f from gas source 7 containing hydrogen gas. Hydrogen radicalgenerating means 120 also includes a microwave oscillator 21 forgenerating microwaves of 2.45 GHz, a waveguide 22 for guiding themicrowaves to the quartz pipe 23 and a plasma generating furnace 24 forgenerating a hydrogen gas plasma in the hydrogen gas passing throughpipe 23. Furnace 24 has cylindrical portions 24a and 24b covering thequartz pipe 23 so that the entire circumference and the total area inthe longitudinal direction of the quartz pipe 23 is irradiated bymicrowaves guided by the waveguide 22.

The thin film formation apparatus 110 also comprises first and secondelectrodes 29 and 27 disposed in opposed relationship within the reactorvessel 26 to define a discharge zone therebetween; the first and secondelectrodes 29 and 27 being formed of a suitable conductive material suchas stainless steel.

The first electrode 29 has openings 29a formed therein permitting thestarting gas supplied through the inlet port 114 to flow into thereactor vessel 26. Openings 29a are provided in large numbers at theupper and lower sections of electrode 29 and in small numbers at thecenter area of electrode 29, as shown in FIG. 4, so that the startinggas supplied from the inlet port 114 is uniformly released along thelength of the substrate 100.

The first electrode 29 is connected to a radio frequency electric source31 through an impedance matching box (not shown) and a blockingcapacitor 30; the RF source 31 (13.56 MHz) being grounded as shown inFIG. 3.

The second electrode 27 includes a rectangular flat portion 27a, ismounted on the bottom inner wall of the reactor vessel 26, and isgrounded as shown in FIG. 3. A substrate 100 is placed on flat portion27a at a predetermined location, and portion 27a is heated by a suitableelectric heater 28 incorporated therein. Heater 28 is driven by a powersource 28a.

A photosensitive member of the construction shown in FIG. 1 may beformed by the following method in the thin film formation apparatusshown in FIG. 3 and FIG. 4.

First, a substrate 100 of aluminum Al, etc. is placed under atmosphericconditions on second electrode 27 which is located in facing, opposedrelationship with respect to first electrode 29 to form a depositionspace 34 therebetween within the reactor vessel 26.

Next, air is drawn from the reactor vessel 26 through the outlet port116 by the vacuum pumps 32, 33 until the pressure in the reactor vessel26 is lower than 0.2 Torr. Then the substrate 100 is heated to apredetermined temperature (250° C.) by the electric heater 28 while astarting gas is continuously introduced into the reactor vessel 26through the inlet port 14 and the opening holes 29a so that the pressuretherein is maintained at a predetermined level (0.2 Torr). The vacuumpumps 32, 33 are continuously driven.

Thereafter, only the flow regulators 5a, 5b are actuated and thereforeonly disilane Si₂ H₆ from the gas source 1 and diborane B₂ H₆ from thegas source 6 are introduced to the reactor vessel 26 through the flowregulators 5a, 5e, pipe 118, inlet port 114 and opening holes 29a offirst electrode 29. In this case, the flow rate of disilane Si₂ H₆ is 30SCCM (Standard Cubic Centimeter per Minute: Mass flow rate at 0° C., 1atm) and the flow rate of diborane B₂ H₆ is 42 SCCM.

Under this condition, a radio frequency (RF) power of 100 W is appliedto the first electrode 29 from the radio frequency source 31. As aresult, the starting gas consisting of disilane Si₂ H₆ and diborane B₂H₆ is decomposed in the deposition space 34 and is formed into a plasma.Thus, an a-Si:H film which is doped with boron (B) to a high degree isformed on the substrate 102 until it attains a thickness of 0.56 μm.This a-Si:H film is the blocking layer 103.

After formation of the blocking layer 103 on the substrate 102, thepressure in the reactor vessel 26 is reduced to about 0.1 Torr andmaintained at such level. Simultaneously with such pressure reductionoperation, flow regulator 5e is adjusted so that the flow rate ofdiborane B₂ H₆ becomes 1 SCCM. RF power is 100 W.

An a-Si:H film which is doped with boron (B) to a lesser degree isformed on the blocking layer 103 until it attains a thickness of about3-4 μm. This a-Si:H film is the photosensitive member layer 104.

After formation of the photosensitive member 104, the film formingconditions of the thin film formation apparatus are changed as indicatedbelow and a surface protecting layer having a thickness of 0.18 μm isformed on the photosensitive member 104.

Pressure: 0.1 Torr

Substrate temperature: 250° C.

RF power: 100 W

Flow rate of Si₂ H₆ : 2 SCCM

Flow rate of C₃ H₈ : 20 SCCM

Flow rate of H₂ : 100 SCCM

Microwave power: 380 W

The flow regulator 5e is closed after formation of the photosensitivemember 104 while the pressure is maintained at 0.1 Torr and thesubstrate temperature is maintained at 250° C. Thus, the flow rate ofdiborane (B₂ H₆) becomes 0 SCCM.

Meanwhile, the flow rate of disilane Si₂ H₆ from the gas source 1 is setat 2 SCCM by the flow regulator 5a, and the flow of propane C₃ H₈ fromthe gas source 2 to is set at 20 SCCM by the flow regulator 5b. Thedisilane Si₂ H₆ and propane C₃ H₈ are introduced into the reactor vessel26 as the starting gas through the inlet port 114. Simultaneously,hydrogen gas H₂ from the gas source 7 is also introduced into thereactor vessel 26 by flow regulator 5f through the hydrogen gasintroducing pipe 25 and the inlet port 115. The flow rate of H₂ is setat 100 SCCM.

Under this condition, a radio frequency power of 100 W is applied to thefirst electrode 29 from the radio frequency electric source 31 andsimultaneously or immediately after such application, a microwave powerof 380 W is supplied to the microwave oscillator 21.

When a predetermined RF voltage is applied between the first and secondelectrodes 29 and 27 by the RF electric source 31 to cause an RFdischarge therebetween, the electrons generated by the RF dischargecollide with the starting gas molecules so that a plasma zone 34 isformed between the first and second electrodes 29 and 27. At thebeginning of the RF discharge, the electrons, which are vibrated in thevicinity of the first electrode 29, are captured by the first electrode29 due to the existence of the blocking capacitor 30, so that thepotential of the first electrode 29 is self-biased toward the negativeside.

The hydrogen gas in the quartz pipe 23 introduced through hydrogen gasintroducing pipe 25 of quartz pipe 23 is sent past the waveguide 22 andbecomes plasma and then hydrogen radicals (.H) 10 due to the microwaveenergy provided in the plasma generating furnace 24.

The hydrogen radicals (.H) 10 are guided to the plasma zone 34 in thereactor vessel 26.

Thus, a sufficient quantity of hydrogen radicals (.H) 10 is suppliedbetween the first electrode 29 and second electrode 27 and an a-Si_(1-x)C_(x) :H film containing a large amount of carbon (x=0.8) is formed.

Therefore, when the thin film formation apparatus is operated asdescribed above there is sufficient coupling of silicon (Si) withspecies which have lower coupling energies than carbon (C). Accordingly,the a-SiC:H film thus formed is dense and has less dangling Si atombonds.

The a-Si photosensitive member prepared as described above has such goodelectrical characteristics that its charging voltage is 500 V, itsresidual potential is 5 V and its half-value exposure is 1.0 μJ/cm².

Moreover, this a-Si:H photosensitive member does not cause blurring evenwhen exposed to an ambient temperature of 35° C. and 85%RH and hasexcellent moisture proof characteristics.

The a-SiC:H film of the invention will be understood more readily byreference to the following additional examples; however, these examplesare intended to illustrate the invention and are not to be construed tolimit the scope of the invention.

EXAMPLE 1

After formation of the blocking layer 103 and photosensitive member 104on the substrate 100 by the method described above using the thin filmformation apparatus shown in FIG. 3 and FIG. 4, a surface protectinglayer 105 is formed using the film forming conditions as indicated byTable 1.

                  TABLE 1                                                         ______________________________________                                        Gas Flow Rate (SCCM)                                                          No      Si.sub.2 H.sub.6                                                                      C.sub.3 H.sub.8                                                                         H.sub.2                                                                            Flow rate ratio r                              ______________________________________                                        C2-2    5        5        100  0.50                                           C2-1    2.2     10        100  0.82                                           C2-3    2.2     20        100  0.90                                           Common conditions:                                                            Pressure: 0.2 Torr                                                            RF power: 100 W                                                               Microwave power: 380 W                                                        Substrate temperature: 250° C.                                         r = C.sub.3 H.sub.8 /(C.sub.3 H.sub.8 + Si.sub.2 H.sub.6)                     ______________________________________                                    

Table 2 indicates that electrical characteristics of the a-Siphotosensitive member formed under the film forming conditions describedabove.

    ______________________________________                                             Charging                                                                      voltage                                                                       (corotron Charging Residual                                                                             Dark attenu-                                                                           Content                                    voltage   capability                                                                             voltage                                                                              ation time                                                                             of car-                               No   (KV)) (V) (V/μM)                                                                              (V)    (S)      bon (x)                               ______________________________________                                        C2-2 125 (+8.0)                                                                              32.3     3      27       0.3                                   C2-1 130 (+9.5)                                                                              32.7     8      30       0.45                                  C2-3 190 (+9.0)                                                                              44.9     9      65       0.7                                   ______________________________________                                    

The a-Si:H photosensitive member of sample No. C2-3 does not generateblurring under atmospheric conditions of 35° C. and 80%RH. On the otherhand, sample No. C2-2 generates blurring and sample No. C2-1 sometimesgenerates blurring.

For purposes of comparison, an a-Si photosensitive member was alsomanufactured under the same film forming conditions as that for thesample No. C2-3 using the prior art RF-CVD apparatus shown in FIG. 2.

Such a-Si photosensitive member provides a maximum charging capabilityof only 20 V/μm.

EXAMPLE 2

Table 3 compares the physical characteristics of a-SiC:H films directlyformed on the flat surface 100 by the film formation apparatus (HR-CVD)shown in FIG. 3 and FIG. 4 and the RF-CVD apparatus of the prior artshown in FIG. 2.

                  TABLE 3                                                         ______________________________________                                        Film forming system                                                                             HR-CVD    RF-CVD                                            (Sample No.)      (Cl-8M)   (Cl-9H1)                                          ______________________________________                                        E.sub.gopt (eV)   2.52      2.53                                              B value (cm.sup.-1/2 eV.sup.-1/2)                                                               600       400                                               Contact angle (deg)                                                                             84        70                                                Film forming conditions:                                                      Pressure: 0.2 Torr                                                            Substrate temperature: 250° C.                                         RF power: 100 W                                                               Flow rate of Si.sub.2 H.sub.6 : 2.2 SCCM                                      Flow rate of C.sub.3 H.sub.8 : 20 SCCM                                        Flow rate of H.sub.2 : 100 SCCM                                               Microwave power: 380 W (HR-CVD only)                                          r: 0.9                                                                        ______________________________________                                    

The carbon contents of these samples can be considered to be almostequal from the value of E_(gopt). The B value of the film manufacturedby the HR-CVD apparatus is larger than that of the film manufactured bythe RF-CVD apparatus and the contact angle thereof is also largerbecause the density of the film has been increased by the introductionof hydrogen radicals into the deposition space.

EXAMPLE 3

Table 4 shows a comparison between a sample No. C1-3 manufactured byintroducing propane C₃ H₈ together with disilane Si₂ H₆ into the reactorvessel 26 through the pipe 118 using the thin film formation apparatusshown in FIG. 3 and FIG. 4 and a sample No. C1-4 manufactured byintroducing propane C₃ H₈ together with hydrogen H₂ into the end 23b ofthe quartz pipe 23 and thus into the reactor vessel 26. FIG. 5 is aschematic diagram explaining the methods for introducing propane C₃ H₈,FIG. 5(a) shows the situation where disilane Si₂ H₆ and propane C₃ H₈are supplied together through the pipe 118 and inlet port 114, whileFIG. 5(b) shows the situation where propane C₃ H₈ is supplied through apropane introducing pipe 25b connected to the end 23b of the quartz pipe23.

                  TABLE 4                                                         ______________________________________                                        Introducing system a       b                                                  (Sample No.)       (Cl-3)  (Cl-4)                                             ______________________________________                                        E.sub.gopt (eV)    2.12    2.12                                               B value (cm.sup.-1/2 eV.sup.-1/2)                                                                715     699                                                Contact angle (deg)                                                                              73      59                                                 ______________________________________                                    

This comparison suggests that the introducing system in FIG. 5(a)provides better results. In the introducing system shown in FIG. 5(b),C₃ H₈ is decomposed to form carbon atoms (C) within quartz pipe 23 andthus the amount of CH_(n) and C₂ H_(n) radicals is increased. In suchcase, the density of film is probably decreased because the amount ofhydrogen available to form Si--H at the outermost surface of the a-SiC:Hfilm formed on the substrate 100 in the deposition space 34 isdiminished and therefore the number of dangling Si atom bonds increases.

Film forming conditions:

Pressure: 0.2 Torr

Substrate temperature: 250° C.

RF power: 100 W

Flow rate of Si₂ H₆ : 3 SCCM

Flow rate of C₃ H₈ : 7 SCCM

Flow rate of H₂ : 100 SCCM

Microwave power: 360 W

r: 0.7

EXAMPLE 4

FIG. 6 illustrates a thin film formation apparatus for manufacturing aphotosensitive member drum. The second electrode 27 of the thin filmformation apparatus (HR-CVD) of FIG. 3 and FIG. 4 is formed into acylinder so that it can be rotated by a drive motor (not shown). Thesubstrate 100Z also is in cylindrical form and the first electrode 29 isarcuate and extends around almost the entire circumference of the secondelectrode 27. A hydrogen radical introducing part 35 is provided tointroduce hydrogen radicals supplied from the inlet port 115 and todistribute the same uniformly along the length of the substrate 100.This hydrogen radical introducing part 35 is formed in the same shape asthe first electrode 29 shown in FIG. 4.

An a-SiC:H film is formed using the following film forming conditions inthe thin film formation apparatus of FIG. 6. The a-SiC:H film is formedby first depositing a blocking layer 103 and a photosensitive layer 104on the cylindrical substrate 100Z. The blocking layer 103 andphotosensitive layer 104 are deposited using the same method andconditions described previously. The blocking layer 105 is thendeposited as described below.

Film forming conditions:

Pressure: 0.2 Torr

Substrate temperature: 250° C.

RF power: 100 W

Flow rate of Si₂ H₆ : 2.2 SCCM

Flow rate of C₃ H₈ : 10 SCCM

Flow rate of H₂ : 200 SCCM

Microwave power: 540 W

r: 0.8

Table 5 shows the characteristics of the a-Si photosensitive member thusformed.

                  TABLE 5                                                         ______________________________________                                        Charging voltage (V)                                                                           360 (for a current of 120 μA                                               flowing into the drum)                                       Residual voltage (V)                                                                           5                                                            Charging capability (V/μm)                                                                  6.7                                                          Contact angle (deg)                                                                            80 to 85                                                     Moisture proof   No blurring under atmospheric                                characteristics  conditions of 35° C. and 80% RH                       Content of carbon (x)                                                                          0.45                                                         ______________________________________                                    

This a-Si photosensitive member drum shows high water repellentcharacteristics and a contact angle in the range of 80°-85°, although itdiffers slightly depending on position. This a-Si photosensitive drumassures good printing results without "blurring" under atmosphericconditions of 35° C. and RH even after continuous corona irradiation fortwo hours and then leaving the drum in the humid atmosphere overnight.

EXAMPLE 5

The a-SiC:H films are formed directly on Al substrates under the samefilm forming conditions for the purpose of investigating an a-SiC:H film(hereinafter referred to as a-SiC:H 1) formed using the thin filmformation apparatus (HR-CVD) shown in FIG. 3 and FIG. 4 and an a-SiC:Hfilm (hereinafter referred to as a-SiC:H 2) formed using the RF-CVDapparatus of the prior art.

Film forming conditions:

Pressure: 0.2 Torr

Substrate temperature: 250° C.

RF power: 100 W

Flow rate of Si₂ H₆ : 2.0 SCCM

Flow rate of C₃ H₈ : 10 SCCM

Flow rate of H₂ : 200 SCCM

Microwave power: 500 W (HR-CVD only)

Table 6 shows the characteristics of the a-SiC:H films manufactured asdescribed.

                  TABLE 6                                                         ______________________________________                                                        a-SiC:H 1                                                                             a-SiC:H 2                                             ______________________________________                                        E.sub.gopt (eV)   2.21      2.14                                              B value (0 cm.sup.-1/2, eV.sup.-1/2)                                                            674       641                                               Contact angle (deg)                                                                             79        72                                                Content of carbon (x)                                                                           0.45      0.45                                              ______________________________________                                    

To further investigate the differences between these two kinds ofa-SiC:H films, they were subjected to corona irradiation for 60 minutesusing a corona charger under atmospheric conditions of 35° C. and 80%RHand the surface conditions were measured by the high sensitivityreflection method (IR-RAS) using a Fourier's transformation infraredspectroscopic analyzer (FT-IR) (JIR-3505 manufactured by JEC).

FIG. 7 is a graph showing the results of the measurements by IR-RAS.Compared with the a-SiC:H 2 film, the a-SiC:H 1 film exhibits about 1/3as much absorption of H--OH and oxidation of Si to form Si--O--Si,Si--OH, etc.

Laser Raman spectroscopic measurement was also used for investigatingthe differences of the constitutions of such a-SiC:H films.

FIG. 8 is a schematic diagram to illustrate the Laser Raman spectroscopymeasurement procedure as used for measuring the density of an a-SiC:Hfilm. The laser oscillated from the Ar⁺ 488 nm oscillator 21 forexcitation laser oscillation passes an interference filter 22 and entersa sample cell 25 to which Ar gas is supplied with an incident angle of45° by way of a mirror 23₁, a slit 24 and a mirror 23₂. Sample 50 is afilm deposited on a substrate 100. The Raman scattering beam emittedfrom the sample 50 is sent to a spectrometer 28 by way of a slit 26₁, acondenser lens 27 and a slit 26₂ and is converted to the spectrum in adata processing unit 29. 30 designates a photomultiplier.

For the measurement of a-SiC:H films, a laser Raman spectrometermanufactured by JEC has been used.

The spectrum result obtained by such measurement of an a-SiC:H filmexhibits both a TO peak (about 488 cm⁻¹) and a TA peak (about 150 cm⁻¹).The TO/TA peak ratio provides an indication of disturbances in thesymmetry of Si coupling or constitution of the film and larger values ofsuch ratio suggest a higher density of constitution.

FIG. 9 shows the results of laser Raman spectroscopy measurements andcompares a high density a-SiC:H 1 film with a conventional a-SiC:H 2film. The TO/TA ratio of a-SiC:H 2 is 1.8 and that of a-SiC:H 1 is 2.4,thus proving that the latter has a denser constitution. This effect isbelieved to be the result of phenomena explained hereinbelow.

When carbon is contained in a-Si:H, the Si network is disturbed to acertain degree. As a result, the reactivity of Si at the surface of ana-SiC:H film increases, and the surface Si is oxidized by ozone (O₃)generated by corona irradiation and is easily changed to Si--O--Si andSi--OH. However, it is believed that the reactivity of surface Si issuppressed in high density a-SiC:H films and moreover, that surfaceabsorption and oxidation by corona irradiation under conditions of highhumidity can be eliminated, thus preventing blurring.

In order to investigate the relationship between the carbon content (x)of a-SiC:H films and the TO/TA ratio thereof, a-SiC:H films of differentcarbon content (x) have been manufactured by varying the flow rates ofdisilane Si₂ H₆, propane C₃ H₈ and hydrogen H₂.

Table 7 shows relationships among flow rate, carbon content (x) andcontact angle.

                  TABLE 7                                                         ______________________________________                                        Flow Rates     Content of                                                     (SCCM)         carbon    Contact angle (deg)                                  No.  Si.sub.2 H.sub.6                                                                      C.sub.3 H.sub.8                                                                      H.sub.2                                                                            (x)     a-SiC:H 1                                                                             a-SiC:H 2                            ______________________________________                                        1    5        5     200  0.3     70      60                                   2    2.2     10     200  0.45    80      77                                   3    2.4     10     200  0.6     81      80                                   4    2.2     20     200  0.7     82      80                                   ______________________________________                                    

FIG. 10 is a graph showing the relationship between carbon content (x)and TO/TA ratio. As will be understood from FIG. 10, the a-SiC:H 1 filmhas a TO/TA ratio of 2.0 or higher and has a film density that is higherthan that of the a-SiC:H 2 film.

As a result of image formation tests under an atmosphere of 35° C. and80%RH using an a-Si photosensitive member having an a-SiC:H 1 film asthe surface protecting layer, it was determined that an a-Siphotosensitive member having the surface protecting layer with a carboncontent of 0.3 generated blurring, but when the other protecting layerswere used with the a-Si photosensitive member blurring did not occur.

When the carbon content x of a-Si_(1-x) C_(x) :H film is set at x≧0.8,carbon-rich constitution is obtained, lowering insulationcharacteristics and charging capability.

Therefore, the optimum hydrogenated amorphous silicon carbide expressedby the general formula a-Si_(1-x) C_(x) :H should have TO/TA ratio of2.0 or more, wherein TO is the peak amplitude that appears in thevicinity of 480 cm⁻¹ and TA is the peak amplitude that appears in thevicinity of 150 cm⁻¹ as observed by laser Raman spectroscopy measurementusing the excitation laser of Ar⁺ 488 nm, and a carbon content (x) inthe range of 0.4≦x≦0.8.

Measurement values in Example 1 to 5 were determined using the measuringmethods described below.

(1) Contact angle:

20 μl of pure water was dropped on a horizontal sample using amicrocylinder (type 4780, manufactured by Eppendorno) and pictures ofthe drops were taken by a camera (RZ67, manufactured by Mamiya) straightfrom the side and the formula 2(h/d)=tanθ was used to calculate theangle from the width d of the drops and the height h from which theywere dropped.

(2) Measurement of E_(gopt) :

Absorption at the wavelength of 200˜800 nm of an a-SiC:H film depositedon the substrate is measured using an ultraviolet visiblespectrophotometer (UV-3400, manufactured by Hitachi). The optical bandgap (E_(gopt)) and value of B are obtained using the formula (1) below.The value of B indicates the gradient of the tail portion of the band asa criterion of film density.

    α(ω)=B(hω-E.sub.gopt).sup.2 /hω    (1)

Here, α(ω); absorption coefficient,

ω; number of variations

h; Planck's constant

(3) Charging voltage:

This value is obtained using a paper analyzer (Model SP-428,manufactured by Kawaguchi Electric).

(4) Residual potential:

A sample charged by the Model SP-428 paper analyzer identified above wasirradiated with a light beam having a wavelength of 675 nm and anintensity of 0.476×10² mW/m² and the potential for minimum charging isdefined as the residual potential Vr.

(5) Dark attenuation time:

The time until the charging voltage is reduced to one half after asample is charged using the Model SP-428 analyzer is defined as the darkattenuation time t_(1/2).

FIG. 11 is a schematic diagram illustrating a second embodiment of athin film formation apparatus of the invention. In the embodiment shownin FIG. 11, a thin film formation apparatus provides a hydrogen radicalintroducing unit 42, which introduces the hydrogen radicals (.H)generated by the hydrogen radical generating unit 120 uniformly alongthe length of substrate 100 placed on the second electrode 27 in thereactor vessel 26, and is located between the reactor vessel 26 andhydrogen radical generating unit 120 for FIG. 3 and FIG. 4.

As shown in FIG. 12, hydrogen radical introducing unit 42 includes anouter wall 43 and an inner wall 44 which are concentrically arranged andshaped so as to increase the width of the unit 42 as it approacheselectrode 27. The walls are coupled together with holding rods 45a, 45b,45c and 45d. An end part 42a of the hydrogen radical producing unit 42is connected with the output port of hydrogen radical generating unit120 at the end of quartz pipe 23. The entire hydrogen radicalintroducing unit 42 is arranged within vacuum vessel 26, while the openend 42b of the hydrogen radical introducing unit 42 is provided infacing relationship to the deposition space 34.

The hydrogen radicals generated in the plasma generating furnace 24during film formation are spread uniformly in the deposition space 34 bythe outer wall 43 and inner wall 44 of the hydrogen radical introducingunit 42. In this case, the distribution of the radicals can be adjustedby adjusting the opening diameter d₁ of end part 43a of outer wall 43,the opening diameter d₂ of the end part 44a of inner wall 44, theopening diameter D₁ of end part 43d of outer wall 43 and/or the openingdiameter D₂ of end part 44d of inner wall 44.

As described, the supply of hydrogen radicals to the deposition space 34is conducted uniformly, and accordingly uniformity of film quality ofthe hydrogenated amorphous silicon carbide a-SiC:H film formed on thesubstrate 100 can be realized.

FIG. 13 is a schematic diagram of a third embodiment of the invention.This embodiment illustrates an application of the apparatus of FIG. 12for a drum type substrate.

In this embodiment, the first electrode is formed from a pair of dividedelectrodes 29b, 29c, each of which is connected with an RF source 31.Moreover, heater 52 is in a cylindrical form. The substrate 102 is inthe form of an aluminum tube having a diameter of 80 mm and a length of260 mm for carrying the a-Si photosensitive drum.

As shown in FIG. 14, the hydrogen radical introducing unit 51 is formedby joining outer walls 55a, 55b and inner walls 56a, 56b with sideplates 53a, 53b to provide flow channels 50e, 50f which are rectangularin cross-sectional configuration and expand in width in a directiontoward the depositing zone 54. The hydrogen radical introducing unit 51is connected to the end part 23a of the quartz pipe 23 which is providedwith a rectangular cross-sectional configuration and is positioned toface toward the deposition space 54 within the vacuum vessel 26. Thehydrogen radicals are supplied from the openings 50a, 50d at the end 51aof hydrogen radical introducing unit 51 to the deposition space 54through the channels 50e formed between outer wall 55a and inner wall56a, and between outer wall 55b and inner wall 56b and the channel 50fformed between inner wall 56a and 56b. The radicals are received inchannels 50e through openings 50b and in channel 50f through opening50c.

For film formation, the starting gas (Si₂ H₆ 2 SCCM and C₃ H₈ 10 SCCM)is introduced to the reactor vessel 26 through openings 29a in the firstelectrode 29b from the inlet port 114, and hydrogen (H₂ 200 SCCM) isintroduced from the hydrogen gas introducing unit 25. An a-SiC:H film isformed under the conditions that the temperature of substrate 102 is250° C., the pressure in the reactor vessel 26 is 0.2 Torr, the RF poweris 100 W and the microwave power is 540 W.

Table 8 shows the differences in the film at the center and the endportions of the cylindrical substrate 102 depending on whether or notthe hydrogen radical introducing unit 51 is used.

                  TABLE 8                                                         ______________________________________                                        End part     Hydrogen radical introducing unit 51                             Center       Operating     Not Operating                                      ______________________________________                                        Uniformity                                                                             Center  0.46 μm/h  0.46 μm/h                                   of film  End     0.46          0.44                                           forming rate                                                                           Part                                                                 Uniformity                                                                             Center  2.21 eV       2.21 eV                                        of optical                                                                             End     2.21          2.12                                           band gap Part                                                                 E.sub.gopt                                                                    Uniformity                                                                             Center  674 cm.sup.-1/2 · eV.sup.-1/2                                                      674 cm.sup.-1/2 · eV.sup.-1/2         of       End     670           570                                            B value  Part                                                                 ______________________________________                                    

The hydrogen radicals 10 have natural life times, and when the distanceD between the deposition space 34 and the hydrogen radical generatingarea in furnace 24 becomes greater, the quantity of hydrogen radicalsreaching the deposition space 34 becomes reduced. Thus, as shown in FIG.15, when the distance D becomes greater, the intensity of emitted lightis lower and the concentration of hydrogen radicals is alsocorrespondingly lower.

In the system of FIG. 13, a large scale apparatus including a waveguide22, a plasma generating furnace 24 and a quartz pipe 23 is used forgenerating hydrogen radicals and accordingly there is a limit to theextent that the distance D can be reduced.

The optical band gap E_(gopt) and the B value relating to film densityare very important considerations for determining the quality of a-SiC:Hfilms, and uniformity in film quality and in film forming rates can beachieved by using the hydrogen radical introducing unit 51. Byexperimentation it has been determined that the ratio h₂ /h₁ in FIG. 14may be varied from 0.1 to 0.5 and that the ratio H₂ /H₁ may be variedfrom 0.3 to 0.7. But, optimum results and the results of Table 8 areobtained when h₂ /h₁ =0.2 and H₂ /H₁ =0.5.

The hydrogen radical introducing unit 51 shown in FIG. 14 can also beused to form a film on a flat substrate 100 in the same way as in thesecond embodiment shown in FIG. 11.

As an alternative-system, microwaves may be supplied directly to thereactor vessel to thereby decompose both the starting gas and thehydrogen gas in the vicinity of the substrate; however, such systemincludes the probability of a deterioration of film quality because thestarting gas is decomposed by the microwaves and the film deposited onthe substrate is also exposed to microwaves.

FIG. 16 shows another embodiment of a thin film formation apparatuswhich is capable of effectively forming a high quality film.

In the embodiment of FIG. 16, hydrogen radicals (.H) 10 are generated inthe reactor vessel 26. In this regard, the hydrogen radical generator 60comprises an antenna 62 connected to the microwave oscillator 21 througha coaxial cable 61, a box type vessel 64 to which the hydrogen gas fromthe source 4 (not shown) is introduced through the hydrogen gasintroducing pipe 63 and a shielding member 66 which shields themicrowaves released to the box type vessel 64 so that the microwaveenergy cannot move toward the substrate 100 through the hydrogen radicalblowing port 65 of the box type vessel 64.

The hydrogen radical generator 60 comprises, as shown in detail in FIG.17, a box type vessel 64 having a blowing port 65, an antenna 62 and ashielding member 66. The vessel 64 has the dimensions of 30 cm (height),3 cm (width) and 5 cm (depth). The gas introducing pipe 63 is connectedto the upper part of the vessel 64 to supply the hydrogen gas to the gasintroducing path chamber 64a formed to extend longitudinally of theheight of the vessel 64. The hydrogen gas thus supplied is thenintroduced into the vessel 64 through opening holes 64b provided in thegas introducing path chamber 64a. Moreover, the coaxial cable 61 isconnected to the vessel 64 and the antenna 62 is formed from a stainlessrod having a diameter of 1.0 mm and which is covered with quartz.Antenna 62 is connected to the coaxial cable 61 and extends verticallyin vessel 64 as can be seen in FIG. 17. Rather than quartz the cover forantenna 62 may be an insulator, fluoric resin, glass or SiC, etc.,including materials which are resistive to heat and do not generate gas.

The shielding member 66 is like a mesh formed of stainless wire having adiameter of 0.5 mm and spaced at intervals of 5 mm, and the same isattached to extend vertically of vessel 64 at the blowing port 65. Thehydrogen radical generator 60 is provided within the reactor vessel 26at a position spaced 100 mm from the substrate 100.

The substrate 100 is set on the second electrode 27 and is held there bya substrate holder that has dimensions of 10×20 (not shown). Electrode27 is grounded and film formation on substrate 100 is conducted usingthe following procedures.

Microwaves generated by microwave oscillator 21 are sent to antenna 62by coaxial cable 61, and H₂ gas introduced through gas introducing pipe63 is decomposed by the microwaves generated by the antenna 62 to formhydrogen radicals 10. The hydrogen radicals 10 are attracted to thesubstrate 100. Since shielding member 66 is attached to the hydrogenradical blowing port 65 of hydrogen radical generator 60, the microwavesare shielded by the shielding member 66 and do not leak to the outsideof vessel 64. Meanwhile, the starting gas (Si₂ H₆ +C₃ H₈) is introducedthrough the starting gas introducing unit 114 and blows into depositionspace 34. This starting gas is decomposed by the RF discharge generatedbetween electrodes 29, 27 by the RF power from the RF source 31 and isdeposited as an a-SiC:H film on the substrate 100 heated by the heater28. The internal pressure in vacuum vessel 26 is adjusted by theexhausting systems 32, 33. While the starting gas is decomposed anddeposited by high frequency discharge, the film surface is covered byhydrogen radicals 10 generated from the hydrogen radical generator 60and thereby the structural density of the a-SiC:H film is improved.During formation of the film, the distance between the hydrogen radicalgenerator 60 and the deposition space 34 (substrate 100) can be as shortas about 100 mm without decomposition of starting gas by microwaves andwithout exposure of the substrate to the microwaves. Thus, leakage ofmicrowaves from the hydrogen radical generator 60 is presented asdescribed above and hydrogen radicals can be sent effectively to thedeposition space. Moreover, the silicon system powder and film generatedthrough decomposition of starting gas by RF discharge do not readilyadhere to microwave antenna 62. The silicon powder is prevented fromadhering to the antenna 62 by allowing the H₂ gas to flow from thevicinity of antenna 62 at a flow rate that is 10 to 1000 times as greatas that of the starting gas and this effect becomes more apparent as aresult of the use of the shielding member 66.

Actual film forming conditions used with such apparatus and thecharacteristics of the film thus formed are as follows.

The film forming conditions are that the pressure is 0.2 Torr, thesubstrate temperature is 250° C., the RF power is 100 W, the Si₂ H₆ flowrate is 2 SCCM, the C₃ H₈ flow rate is 10 SCCM, the H₂ flow rate is 200SCCM and the microwave power is 500 W.

FIG. 18 is a graph showing the results of Raman spectroscopy measurementof an a-Si_(1-x) C_(x) :H film (x=0.6) formed using such conditions. TheTO/TA peak intensity ratio represents small distortions in the Si--Sicoupling structure in the film and in the symmetry thereof and largerTO/TA ratios indicate smaller distortions. From FIG. 18, it can be seenthat the a-SiC:H film formed using the apparatus of FIGS. 16 and 17 ofthe present invention has a higher TO/TA ratio, is more dense and hasbetter film qualities than the film formed by the prior art.

In the foregoing example, a flat type substrate was used and it is alsopossible to form a film on a substrate attached on a cylindricalsubstrate holder. In this case, the substrate is rotated duringformation of the film. An a-Si photosensitive member using an a-SiC:Hprotective layer by an apparatus using such cylindrical substrate has acharging capability of 55 V/μm, does not show any blurring when leftovernight in an atmosphere at 35° C. and 88%RH after continuous coronairradiation under the same conditions and also exhibits good moistureproof characteristics.

In the above procedures, a mesh shielding member is used, but the meshmay be replaced by other members for shielding the microwaves, such as,for example, rod like lead wires placed at certain intervals.

FIG. 19 is a schematic diagram illustrating a fifth embodiment of theinvention. This embodiment differs from the third embodiment illustratedin FIG. 13 in that a plurality of hydrogen radical generating units areprovided so that the hydrogen radicals are sent to the substrate anddeposition space from two or more directions through the inlet ports115-1, 115-2.

The first and second hydrogen radical generating units 120-1, 120-2 havethe same basic construction as the hydrogen radical generating unit 120described in connection with FIG. 13 and the hydrogen radicalintroducing units 51-1, 51-2 are each the same as the unit 51 shown inFIG. 14.

In the embodiment at FIG. 19, since the hydrogen radicals are introducedfrom two or more directions to the substrate or deposition space, thehydrogen radicals are applied uniformly and therefore the density of thea-SiC:H film is much improved.

The following film forming conditions were used to form a surfaceprotecting layer using the apparatus of FIG. 19.

Pressure: 0.2 Torr

Substrate temperature: 250° C.

RF power: 100 W

Flow rate of Si₂ H₆ : 2 SCCM

Flow rate of C₃ H₈ : 10 SCCM

Flow rate of H₂ : 200 SCCM

Microwave power: 500 W

For the total of 200 SCCM of H₂, 100 SCCM is respectively suppliedthrough the hydrogen gas introducing pipes 25-1, 25-2 of the first andsecond hydrogen radical generating units 120-1, 120-2. The hydrogen inthe respective streams of gas is decomposed in the plasma generatingfurnaces 24-1, 24-2, and becomes the hydrogen radicals 10 supplied fromboth directions to the substrate 102.

An a-Si photosensitive member comprising a surface protecting layerhaving a thickness of 0.2 μm formed of a-SiC:H under the conditionsdescribed above on a blocking layer of a high B doped a-Si:H film havinga thickness of 0.56 μm and a low B doped a-Si:H film having a thicknessof 10 μm did not generate blurring after continuous corona irradiationfor two hours in an atmosphere of 35° C. and 80%RH and even afterexposing the member overnight to such continuous corona irradiation.

Hydrogen radical introducing units 51-1, 51-2 of the construction shownin FIG. 14 are connected respectively at the end portions of quartzpipes 23-1, 23-2 and the hydrogen radicals 10 generated in the plasmagenerating furnaces 24-1, 24-2 by microwaves supplied from the microwaveoscillators 21-1, 21-2 through the waveguides 22-1, 22-2 are distributedvertically over the substrate 102 and flow uniformly into the depositionspace 34. A comparison of the TO/TA ratios for cases where the hydrogenradical introducing units 51-1, 51-2 are used and where such units arenot used is made in Table 9.

                  TABLE 9                                                         ______________________________________                                                   Units used                                                                            Units not used                                             ______________________________________                                        Upper part   2.0       2.3                                                    Center       2.4       2.4                                                    Lower part   1.9       2.2                                                    ______________________________________                                    

From Table 9, it is apparent that differences between the TO/TA ratiosat the upper part, center part and lower part of the substrate can bereduced by using the opposed introducing units 51-1, 51-2.

FIG. 20 is a schematic diagram illustrating a sixth embodiment of theinvention. The apparatus of FIG. 20 is different from the fifthembodiment shown in FIG. 19 in that a single microwave oscillator isused in common for two hydrogen radical generating units 120-1, 120-2.

As shown in FIG. 20, the microwave output from single microwaveoscillator 21 passes an isolator 72 and is then divided by a microwavedistributor 71 to the waveguides 22-1, 22-2 of the hydrogen radicalgenerating units 120-1, 120-2.

The waveguides 22-1, 22-2 are provided with power motors 73-1, 73-2 andmatching units 74-1, 74-2. Moreover, the microwave power of microwaveoscillator 21 is 800 W.

With such construction, since the period of the microwave oscillator 21is the same in both hydrogen radical generating units 120-1, 120-2,reflections caused by deviations of period increase and therefore theplasma can be kept in a stable condition.

Accordingly, this embodiment can be used to provide a stable filmforming operation for a long period of time.

In the arrangement shown in FIG. 20, the surface protecting layerforming conditions are set such that the pressure is 0.2 Torr, thesubstrate temperature is 250° C., the RF power is 100 W, the Si₂ H₆ flowis 2 SCCM, the C₃ H₃ flow is 10 SCCM, the H₂ flow is 200 SCCM and themicrowave power is 800 W. Moreover, 100 SCCM of H₂ is supplied from eachof the two directions for the total flow of 200 SCCM of H₂ as in thecase of the embodiment of FIG. 5.

As a result, reflection was reduced to 1/2 to 1/3 of that which wasexperienced using two microwave oscillators and unstable operationcreated by senodic plasma generation is eliminated. Thus, continuousfilm formation for a long period of time can now be realized.

The blocking layer is formed on the cylindrical Al substrate as a higherB doped a-Si:H film having a thickness of 0.56 μm, while thephotosensitive layer is formed as a lower B doped a-Si:H film having athickness of 10 μm and the surface protecting layer is deposited to athickness of 0.15 μm under the film forming conditions described above.The a-Si:H film having a surface protecting layer thusly formed did notgenerate blurring after continuous corona irradiation for two hours inan atmosphere of 35° C. and 80%RH and even after overnight exposure tosuch continuous irradiation.

FIG. 21 illustrates a modification of the thin film formation apparatus110 of FIG. 11. In FIG. 21, the features similar to those of FIG. 11 areindicated by the same reference numerals. The modified apparatus is thesame as shown in FIG. 11 except that the first electrode 29 is replacedwith a hollow cathode electrode 29A and the hydrogen radical introducingunit 51 has the structural configuration illustrated in FIG. 14.

In this embodiment, the hollow cathode electrode 29A includes arectangular flat portion 29h and an upright portion 29g integrallyprojected from the flat portion 29h along the longitudinal axis thereof.A rectangular hollow space 29j formed in upright portion 29g extendsthrough the flat portion 29h and opens at the discharge surface thereof.

As can be seen in FIG. 21, the upright portion 29g has a plurality ofopening holes 29i formed at the head 29l thereof in vertical alignmentwith one another. The electrode 29A is suspended from the side wall ofthe reactor vessel 26.

In particular, the head 29l of the upright portion 29g projects throughthe side wall of the reactor vessel 26 and is attached to the side wallof the reactor vessel 26 through the intermediary of an insulator (notshown), and a header element 114a by which the inlet port 114 is definedis mounted on the head 29l of the upright portion 29g in such a mannerthat the inlet port 114 is in communication with a head space 29k whichin turn communicates with the hollow space 29j through the opening holes29i.

In operation, air is first drawn from the reactor vessel 26 through theoutlet port 116 by the vacuum pumps 32, 33 until the pressure in thereactor vessel 26 is lower than 10⁻³ Torr. Substrate 100 is then heatedto a predetermined temperature by electric heater 28 while the startinggas is continuously introduced into the reactor vessel 26 through theinlet port 114, the opening holes 29i, and the hollow space 29j, so thatthe pressure in vessel 26 is maintained at a predetermined level of fromabout 0.01 to about 0.3 Torr. The vacuum pumps 32, 33 are continuouslydriven.

A predetermined RF voltage is then applied between the first and secondelectrodes 29A and 27 by the RF electric source 31 so as to cause an RFdischarge therebetween, and the electrons generated by the RF dischargecollide with the starting gas molecules so that a plasma zone is formedbetween the first and second electrodes 29A and 27. At the beginning ofthe RF discharge, the electrons which vibrate in the vicinity of thefirst electrode 29A are captured by the first electrode 29A due to theexistence of the blocking capacitor 30, so that the potential of thefirst electrode 29A is self-biased toward the negative side. If the flatportion of second electrode 27 which faces portion 29h of firstelectrode 29A is wider than flat portion 29h of the first electrode 29A,i.e., if the area of the flat portion of electrode 27 that faces portion29h is smaller than the area of flat portion 29h, the capture ofelectrons by first electrode 29A is facilitated.

When the first electrode 29A becomes saturated with captured electrons,the first and second electrodes 29A and 27 behave respectively as acathode and an anode that have a direct current voltage appliedtherebetween, so that the electrons existing in the hollow space 29j arerapidly vibrated by the electrical repulsion which the electrons receivefrom the wall of the hollow space.

Thus, the probability of collision between the electrons and thestarting gas molecules in the hollow space 29j is considerably enhanced,so that a high density plasma is generated in the central portion of thedischarge zone, which is in the vicinity of the opening of hollow space29j.

As a result, the starting gas is introduced directly into a high densityplasma and the active species are more efficiently dissociated from thestarting gas than would be the case in a conventional RF dischargeplasma-assisted CVD process. Moreover, hydrogen radicals (.H) aregenerated when the microwave oscillator 21 is operated simultaneouslywith the application of RF power, and such radicals are supplied to theplasma zone 34 formed between the first and second electrodes 29A, 27through the hydrogen radical introducing unit 51.

FIG. 22 is a schematic diagram illustrating an eighth embodiment of theinvention. In this embodiment, the hydrogen radical generating unit 120is applied to an optical CVD apparatus 130.

Optical CVD apparatus 130 includes a reactor vessel 26, an introducingpipe 118 for supplying the starting gas to the reactor vessel 26, avacuum pump including a mechanical booster pump 32 connected to theoutlet port 116 and a rotary pump 33 for evacuating the reactor vessel26, a heater 28 for heating the substrate 100, a substrate holder 131which may be rotated together with the heater 28 while it is holding thesubstrate 100 and a light source (not shown) which irradiates thesubstrate holder 131 with light from the exterior of reactor vessel 26to decompose the starting gas introduced from the introducing pipe 118to produce a plasma condition.

The end portion 23a of the quartz pipe 23 of the hydrogen radicalgenerating unit 120 is connected to the vessel 26 of the optical CVDapparatus 130 by way of an inlet port 115 in the same way that suchconnection is made in the case of the embodiment shown in FIG. 4.

Therefore, the optical CVD apparatus 130 can supply a large amount ofhydrogen radicals in the vicinity of the substrate holder 131.

FIG. 23 is a schematic diagram illustrating the configuration of a ninthembodiment of the invention. In FIG. 23, the hydrogen radical generatingapparatus is identified by the reference numeral 70. The components thatare similar to those of the prior art are designated by similarreference numerals as set forth above.

As can be seen in FIG. 24, the hydrogen radical generating apparatus 70in this case is an arc discharge device having a cathode 71, an anode 72and an H₂ gas supply port 73. The cathode 71 and anode 72 are connectedwith the power source 74 and the same are separated by an insulator 75.This embodiment uses an arc discharge hydrogen radical generatingapparatus 70 to generate the hydrogen radicals. The apparatus 70 enablesthe reduction of the discharge sustaining voltage to about 1/10immediately after it increases rapidly when a current higher than theglow discharge is supplied from the power source 74. The cathode 71 isheated until it turns red, and emits hot electrons. Thus, the plasma isin a thermal equilibrium condition wherein the electron temperaturebecomes almost equal to the gas temperature and whereby the H₂ gas isdissociated into an almost 100% plasma condition. A gas having a higherhydrogen radical content than the gas obtained using microwaves can beobtained by extending arc rod 76 up to an area in the vicinity of thesubstrate 100.

In the respective embodiments described above, disilane Si₂ H₆, propaneC₃ H₈ and diborane B₂ H₆ are used as the starting gas, but other gaseswhich may be described by the general expressions Si_(n) H_(3n), C_(n)H_(2n+2) or B_(n) H_(3n) may also be used in combination.

It should also be understood that the foregoing descriptions relate onlyto the preferred embodiments of the invention, and that it is intendedthat the claims should cover all changes and modifications of theexamples of the invention herein chosen for the purpose of thedisclosure, which do not constitute departures from the spirit and scopeof the invention.

We claimed:
 1. Thin film formation apparatus for depositing hydrogenatedamorphous substances on a substrate comprising:a reactor vessel: asubstrate support located in a deposition space in the vessel; astarting gas source for introducing starting gas into said reactorvessel; a plasma generator in said reactor vessel for producing a plasmafrom the starting gas; at least one hydrogen source providing hydrogenfor introduction into the reactor vessel; at least one hydrogen radicalgenerator for generating hydrogen radicals by decomposing the hydrogenintroduced into the reactor vessel; and at least one distributor fordistributing hydrogen radicals uniformly over the substrate, saiddistributor including an elongated hollow hydrogen introducing unithaving spaced apart first and second openings, said first opening beingconnected to the hydrogen source and said second opening beingpositioned adjacent said substrate, said second opening being largerthan said first opening, said unit being shaped so as to expand in widthin a direction from said first opening to said second opening, saiddistributor including at least one internal wall dividing the hollowhydrogen introducing unit into segregated inner and outer flow pathsextending between said openings, whereby a film of amorphous materialforms on a substrate on said support, said hydrogen source, saidhydrogen radical generator and said hydrogen radical distributortogether being arranged and configured to introduce a sufficient amountof hydrogen radicals into said deposition space and to direct theradicals toward a substrate on said support so that a surface of anamorphous film being formed on the substrate is covered uniformly withhydrogen radicals.
 2. Thin film formation apparatus as set forth inclaim 1, wherein said starting gas source includes a source of disilaneand a source of propane.
 3. Thin film formation apparatus as set forthin claim 2, further comprising a source for introducing diborane intosaid reactor.
 4. Thin film formation apparatus as set forth in claim 1,wherein said hydrogen source includes a source of hydrogen gas.
 5. Thinfilm formation apparatus as set forth in claim 1, wherein said plasmagenerator includes a first electrode to which radio frequency power isapplied and a second electrode that is grounded.
 6. Thin film formationapparatus as set forth in claim 1, wherein said hydrogen radicalgenerator includes a microwave oscillator, a waveguide for guidingmicrowaves, a quartz pipe through which said hydrogen is supplied and aplasma generating furnace for applying the microwaves guided through thewaveguide to said quartz pipe.
 7. Thin film formation apparatus as setforth in claim 1, wherein said hydrogen radical generator includes aplurality of hydrogen radical generating units.
 8. Thin film formationapparatus as set forth in claim 7, wherein said hydrogen radicalgenerator includes a microwave oscillator, a plurality of quartz pipesto which said hydrogen is supplied, and a waveguide for guidingmicrowaves from said microwave oscillator to each quartz pipe.